Method and apparatus for applying electronic circuits to curved surfaces

ABSTRACT

An electric circuit is applied to an object having a curved surface. The curved surface of the object is divided into sections, and the circuit is applied one section at a time. The circuit is formed between layers of dielectric material. The dielectric is applied by a computer-controlled device, which controls the position of a spray head and the rotation of the object, such that the spray head is held substantially perpendicular to the surface of the object at all times, and such that a controlled thickness of dielectric material can be deposited. The fine-featured circuits formed by the invention are rugged, and can be used on objects intended to be exposed to harsh environments.

CROSS-REFERENCE TO PRIOR APPLICATION

This is a divisional of U.S. patent application Ser. No. 11/458,307,filed Jul. 18, 2006.

BACKGROUND OF THE INVENTION

This invention relates to the field of electric or electronic circuitswhich are embedded within a dielectric and applied to a curved surface.The invention is especially useful in manufacturing circuits which areintended to operate in harsh environments.

As used herein, the term “circuit” is used in its broadest sense, toinclude any pattern of electrical conductors which accomplishes someuseful object. Such circuits may be active or passive.

One example of the use of the present invention is in the aerospace anddefense industries. It may be necessary to provide circuitry as acovering for the nose cone or radome of a missile, or the nose of anaircraft, to act as shield against radio frequency (RF) energy, or as anelectromagnetic shield. Certain circuit patterns may be capable ofblocking incoming radiation while remaining transparent to radiationtransmitted by an internal antenna within the missile or aircraft. Theinvention is not necessarily limited to use in the above field, butcould be used in other areas.

In the applications described above, the circuit which is applied to anose or nose cone must be extremely rugged, and must withstand extremeconditions of pressure and temperature, without degradation. The circuitmust be capable of withstanding the extreme heat encountered when amissile is traveling at high velocity within the atmosphere, or when aspace vehicle re-enters the atmosphere, or when an aircraft is travelingat high speeds. The circuit must not be affected by other environmentalfactors, such as extreme cold, water, rain, or erosion.

To achieve the desired degree of ruggedness, the circuit is preferablyprovided in the form of a conductive cermet, embedded between layers ofa compatible dielectric material, having the same or betterenvironmental performance as the cermet. In the examples given above,this embedded circuit could be formed on the nose cone or nose, or otherstructure.

A “cermet” is a material containing particles of metal dispersed in aceramic carrier. Initially, the cermet may take the form of a paste.When fired at high temperatures, the metal particles melt and fusetogether, so that the metal particles become an integral electricalconductor which remains conductive when cooled. In this specification,the terms “conductive cermet” and “conductive material” will be used toinclude the cermet paste, although it should be understood that thematerial does not actually become electrically conductive until it hasbeen fired. Examples of such cermet materials, and of their uses, aregiven in U.S. Pat. Nos. 4,897,676 and 6,553,662, the disclosures ofwhich are incorporated by reference herein.

In the specific applications described above, it is important that thecircuit be applied with precision, so that it has uniform geometry andsignificant thickness. When using the techniques of the prior art, suchprecision is virtually impossible to achieve when it is desired to applythe circuit to complex curved substrate surfaces, such as an ogive nosecone.

The present invention provides a practical and economical method andapparatus for applying rugged electronic circuits, of the type describedabove, and to many other types of curved surfaces.

SUMMARY OF THE INVENTION

The present invention includes a method for applying an electricalcircuit to an object having one or more curved surfaces. In general, themethod includes applying a first sealing and smoothing layer ofdielectric material to the surface or substrate, screening or stencilinga layer of electrically conductive patterned or solid material onto thedielectric, the screening or stenciling being performed for a pluralityof sections of the curved surface, each section occupying less than theentirety of the curved surface, and applying a covering layer ofdielectric material onto the conductive material.

It is by dividing the curved surface into relatively small sections thatthe circuit can be precisely screened or stenciled onto the curvedsurface. If the sections are reasonably small, each section of thecurved surface can be considered relatively flat, and it becomes easy toscreen or stencil a circuit onto such section.

The application of dielectric is preferably performed by a computercontrolled spray head, wherein the spray head has three degrees offreedom, and wherein the object can also be rotated under computercontrol. The spray head is positioned so that it is always substantiallyperpendicular to the object being coated. In this way, a thin dielectriclayer, having a very uniform thickness, can be applied to the entiresurface.

The circuit is applied to a section of the curved surface with the aidof a screen or stencil segment, the screen or stencil segmentcorresponding to a section of the curved surface. The screen or stencilsegment may be used multiple times to span the surface of the object.Alternatively, a plurality of different screen or stencil segments canbe used, thereby applying different circuit patterns to differentsections of the curved surface.

In a preferred embodiment, wherein the object comprises an ogive conehaving rotational symmetry, the surface of the object is divided into aplurality of complex tapered sections, and the circuit is first appliedto every other section, and then applied to the remaining sections.Thus, the circuit elements are laid down in a process whereby a firstgroup of sections are interleaved with a second group of sections.

The invention also includes apparatus suitable for performing theabove-described methods. In one preferred embodiment, the apparatusincludes a pivotable fixture, capable of holding a frame which containsa screen or stencil segment, the fixture being movable towards and awayfrom the object. A conductive material can be applied to a section ofthe object when the screen or stencil segment is positioned immediatelyadjacent the object. After the conductive material has been applied, thefixture is moved away from the object, and the object is indexed so thatan untreated section of the surface is accessible by the fixture.

The invention therefore has the primary object of providing a method andapparatus for applying an electrical or electronic circuit pattern to anobject having a curved surface.

The invention has the further object of applying a circuit to a curvedsurface, wherein the circuit is formed between thin, uniform layers of adielectric material.

The invention has the further object of providing methods and apparatusfor applying a rugged electrical circuit to an object which is intendedto be used in a harsh environment.

The invention has the further object of reducing the expense of applyingprecision electric circuits to curved surfaces.

The reader skilled in the art will recognize other objects andadvantages of the present invention, from a reading of the followingbrief description of the drawings, the detailed description of theinvention, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a perspective view of a robotic device, made accordingto the invention, for applying a precisely controlled thickness ofdielectric material onto a curved surface.

FIG. 2 provides a top view of a modified version of the robotic deviceof FIG. 1, showing, in phantom, various positions of a spray head usedfor applying dielectric material onto an ogive curved surface.

FIG. 3 provides a block diagram showing the computer control of therobotic device of either of FIG. 1 or 2.

FIG. 4 provides a perspective view of an apparatus, made according tothe present invention, for applying a screen or stencil segment to asection of a curved surface.

FIG. 5 provides a plan view of a screen or stencil segment used in theapparatus of FIG. 4.

FIG. 6 provides a diagram illustrating a portion of a circuit which isto be applied to a curved surface, using the apparatus and method of thepresent invention.

FIG. 7 provides a perspective view of an ogive radome or nose cone,wherein a circuit has been applied to some sections of the surface ofthe ogive radome, according to the present invention.

FIG. 8 provides a cross-sectional view of the circuit applied to thecurved surface, according to the present invention, the figure showingthe circuit layer sandwiched between layers of dielectric material.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes a method and apparatus for applyingelectrical circuits to objects having curved surfaces. The circuit isintended for use in rugged environments, and is therefore embeddedwithin a dielectric which is applied to the curved surface.

In very general terms, the process of the present invention includespreparing the curved surface to insure that it is smooth, applying oneor more initial layers of dielectric to the surface, applying conductivecermet defining the desired circuit, and applying one or more final orcovering layers of dielectric. The step of applying the conductivecermet is performed for various sections of the surface, each sectioncomprising less than the entirety of the surface.

FIGS. 1-3 illustrate the apparatus for applying the dielectric. FIG. 1illustrates a simple form of a curved object to which a circuit is to beapplied, namely an ogive nose cone 1, mounted for rotation with shaft 5,and supported by supports 2 and 3. Motor/encoder 7 rotates the shaft,and therefore causes rotation of the ogive nose cone, as indicated byarrow 9. In the example represented, the nose cone is the object havingan ogive curved surface, onto which the dielectric material andconductive cermet circuit are to be applied.

A dielectric material is deposited onto the surface of the nose cone byspray head 11, which dispenses dielectric material stored in reservoir13. The spray head and reservoir are mounted on support 15 which isconnected to linear motor/encoder 17, to enable the spray head to movewith one degree of freedom, as indicated by arrow 19. This arrangement,through computer control of the linear position of the spray head, androtational control of the ogive nose cone, provides a basic level ofthickness control of the dielectric layer(s). The programming andcoordinated computer control of the position of a single-axis orthree-axis spray head, and rotation of the ogive nose cone, will beexplained later.

The term “dielectric” includes electrically insulating materials whichare capable of being fired at high temperatures. Examples of dielectricmaterials which can be used, in the present invention, are given in U.S.Pat. Nos. 4,897,676 and 6,553,662, cited above. Dielectrics may besupplied in the form of a slurry which can be sprayed onto a surface, asindicated by FIG. 1.

An ogive nose cone is only one example of an object, having a curvedsurface, onto which the circuit is to be applied. The present inventionis not limited to the case in which the object is an ogive nose cone,but is applicable to many other objects having at least one curvedsurface. It should therefore be understood that whenever an “ogive nosecone” is referenced in this description, other objects having curvedsurfaces could be substituted, with appropriate modifications to thehardware. Such other objects are intended to be included within thescope of the invention.

In the present invention, it is important to apply the dielectric in oneor more layers of uniform thickness. Therefore, the present inventionincludes the step of spraying the dielectric in such a manner that thespray head is always exactly perpendicular to the portion of the surfacebeing sprayed. To maintain this perpendicular orientation, it isnecessary to control carefully the position of the spray head.

FIG. 2 provides a top view of a modified version of the apparatus ofFIG. 1. FIG. 2 shows a nose cone 21, rotated by motor 23, as shown byarrow 22. A linear stage 25, moved by motor/encoder 27, holds spray head29, which is mounted to a second motor/encoder-driven linear stage 35,attached at an approximately right angle to linear stage 25. The secondstage 35 enables the spray head to move in a direction that, with propercomputer control, allows the spray nozzle to maintain a controlleddistance from the ogive nose cone, as the spray nozzle moves along thelinear stage 25. This positional precision is further enhanced bymounting the spray head to a rotational motor/encoder 34 which allowsthe spray head to be rotated such that its nozzle is alwaysperpendicular to the surface of the ogive nose cone. These movements areshown in various positions (illustrated in phantom).

FIG. 2 more explicitly shows the degrees of freedom of the sprayingapparatus. Specifically, the support can move towards or away from thenose cone, as indicated by arrow 31. The support can move parallel, orat an optimized tilted angle, to the axis of the nose cone, as indicatedby arrow 32. Also, the spray head can rotate around post 34, asindicated by arrow 33. Combinations of these three motions, undercomputer control, will enable the spray head to be dynamicallypositioned, during the entire spraying operation, perpendicular to, andat the preferred distance from, the surface of the ogive nose cone, asillustrated in FIG. 2. Note also that the additional degree of freedomprovided by the computer coordination of these three axes with therotational speed of the nose cone allows the spray head shown in FIG. 2effectively to reach virtually any point on the nose cone, and todeposit a very uniform layer of dielectric material.

To explain the above concept further, suppose that the spray head isopposite a portion of the nose cone which has a diameter of 6 inches. Ifthe nose cone is rotating at 60 revolutions per minute, the spray headwill traverse about 6×3.1416×60 or about 1131 inches in one minute. Butif the diameter of the nose cone is only 4 inches, the distance coveredin a minute would be only about 754 inches. So, to obtain the samecoverage of material per unit time, one must slow down the rotationalspeed, when the spray head is opposite the larger diameter portion,and/or speed up the rotational speed when the spray head is opposite thesmaller diameter portion. If the speed is not so regulated, either toomuch or too little dielectric material will be applied.

Also, the system is preferably programmed to move the spray head towardsor away from the nose cone, for further control of the thickness of thedielectric layer. The spray exits the nozzle in the form of a cone, andthe density of the spray is a function of the diameter of this cone aswell as the curvature of the object at the point of application. Withthe nozzle close to the surface, the cone area is small and the spray isconcentrated. When the nozzle is further from the surface, theconcentration of the spray decreases. Thus, the present inventionincludes precise control of the distance of the spray head from thesurface being sprayed, so as to regulate the thickness of thedielectric. The invention therefore includes programmably controllingthe distance between the spray head and the surface being sprayed, thatdistance being varied to maintain the desired thickness of dielectric.

Heater element 36 is incorporated into the apparatus for the purpose ofinitially heating the ogive nose cone to an elevated temperature, andalso for the purpose of accelerating the drying of the dielectricmaterial as it is sprayed onto the ogive nose cone. This combination ofinitial heating of the ogive nose cone, and continued heating duringdielectric application, causes initial dielectric drying on contact, andprevents running of the sprayed dielectric due to gravity or centrifugalforce. To be easily sprayed, it is necessary for the dielectric materialto have a low viscosity, which makes it likely to run or drip. But oncethe material has reached the nose cone, it is desired that the materialdry as quickly as possible. The use of the heater promotes such drying,and also allows for thicker layers of dielectric to be applied per spraycycle.

FIG. 3 provides a block diagram illustrating the computer control of thespraying apparatus. Computer 41 is programmed to control the movement ofmotor/encoder module 42, which rotates the shaft holding the nose cone,and motor/encoder module 43, for controlling the spray head.Motor/encoder 43 may represent more than one motor/encoder, as there maybe separate stages and motor/encoders provided to move the spray headlinearly, and to rotate the spray head around its mounting post. Thecomputer control of the spray head position, in coordination with therotational speed of the ogive nose cone rotational motor, can produce auniform dielectric coating.

As explained above, after the initial layer, or layers, of dielectricare deposited on the object, and fired and cured, the desired circuit isthen applied. FIGS. 4 and 5 illustrate the apparatus for performing thisstep.

In brief, the circuit is screened or stenciled onto the curved surfacein sections. If the curved surface is divided into a sufficiently largenumber of sections, each section can be considered relatively flat, andthe screen or stencil can be deflected by the squeegee used to apply theconductive cermet, to the extent necessary to transfer accurately theconductive cermet pattern to the ogive nose cone. The essence of thisstep is therefore the screening or stenciling of the circuit, onto thecurved surface, in relatively small sections, using one or more screenor stencil segments corresponding to the size of the sections.

FIG. 4 shows the application of one such screen or stencil segment tothe nose cone, and FIG. 5 provides a more detailed top view of thescreen or stencil segment.

The screen or stencil is charged with the conductive cermet andpositioned a small distance above the substrate. A squeegee, or itsequivalent (not shown), is pulled over the top of the screen or stencil.The screen or stencil then deflects, contacting the curved section ofthe substrate, and transfers the cermet from the screen or stencil ontothe substrate. The shape of the individual sections are selected toinsure that the screen or stencil can deflect to the extent necessary toachieve this momentary contact with the substrate, as necessary, totransfer the conductive cermet material from the screen or stencil tothe curved substrate, to achieve the desired pattern.

As shown in FIGS. 4 and 5, a generally rectangular fixture 53 holdsframe 50 which holds screen or stencil segment 51. The frame 50 andscreen or stencil segment 51 are most clearly shown in FIG. 5. Becauseof the curvature of the nose cone, the fixture also has a correspondingcurvature, so that a screen or stencil segment can be brought into closeconformity with the surface to be screened or stenciled. The screen orstencil segment comprises a piece of patterned fine wire screen or, inthe case of a stencil, perforated metal. The screen pattern or stencilperforations define the intended locations and shape of circuitelements. The screen or stencil segment is similar to metal screens orstencils used in the prior art for screening or stenciling a circuitonto a surface, except that the screen or stencil segment is not flat,and will generally not cover, without indexing, all of the intendedcircuit area of the object. The screen or stencil segment and frame areadjustable for alignment, and removable from the fixture 53.

FIG. 4 illustrates the use of fixture 53, holding frame 50 and screen orstencil segment 51, in conjunction with nose cone 52. The fixture 53 ispivotably mounted to shaft 54, mounted on a base, such that the fixturemay be pivoted away from the nose cone, as indicated by arrow 55, orpivoted towards the nose cone, in the direction opposite arrow 55.Motor/encoder 56 is connected to shaft 57, which positions and drivesthe nose cone 52 radially. The motor is used to index the nose cone, asexplained below.

In the example given, the fixture is pivoted towards the nose cone, sothat the screen or stencil 51 lies immediately above and in closeproximity to the surface of the ogive nose cone. A conductive cermetmaterial, which is in the form of a paste, is applied to the screen orstencil with a doctor blade, or its equivalent, so that the cermet isdeposited at the locations corresponding to the openings in the screen,or the holes in the stencil. As the doctor blade or squeegee is drawnover the screen or stencil, along its long dimension, the screen orstencil deflects and comes into contact with, and takes the shape of,the ogive nose cone section outlined by the screen or stencil. Theconductive cermet material is then transferred from the screen orstencil onto the ogive nose cone section and, after the doctor blade orsqueegee passes, the screen or stencil snaps back to its initialoff-contact position just above the surface of the ogive nose cone. Oncea section is completed, the fixture can then be pivoted away from thenose cone, as indicated by arrow 55. The nose cone is then rotated, orindexed, by the motor/encoder, such that a different section of the nosecone surface is presented at a position reachable by the screen orstencil. The fixture can then be recharged with conductive cermet andpivoted again towards the ogive nose cone, and the cermet can bescreened or stenciled onto the new surface section.

It has been found particularly advantageous, in the example of the ogivenose cone, to apply the circuit segments in an interleaved pattern. Thatis, the surface of the nose cone is preferably divided into an evennumber of sections. In the particular example given, that number issixteen sections. The circuit pattern is then laid down onto every othersection. When the circuit has been fired, the intermediate result is asshown in FIG. 7, wherein the circuit has been applied to every othersection. The process is then repeated for the sections not previouslycovered. The advantage of this procedure is that one can make the screenor stencil pattern laid down on the second “pass” either slightly wideror slightly narrower than what was previously applied, so as to achievea perfect match, and to cover the entire surface precisely.

In all cases, the ogive nose cone can be easily indexed, either manuallyor by the motor/encoder 56, so that any desired section of the nose conecan be presented to the apparatus which lays down the circuit.Regardless of whether or not the sections are interleaved, the nose coneis fired after the circuit elements have been laid down, and before afinal coating of dielectric is applied. Such firing causes the metalparticles in the cermet paste to fuse together to define ruggedconductors.

In the example shown, screen or stencil 51 has the shape of arectangular structure which has been tapered. This shape is dictated bythe shape of the surface of the ogive nose cone. It is clear that thesurface of the ogive nose cone can be covered by a plurality of screenshaving the shape shown in FIG. 5, because that surface can be consideredto comprise a plurality of tapered sections. But the exact shape of thescreen or stencil segment can vary considerably. The shape of the screenor stencil segment depends on the shape of the object onto which it isdesired to apply the circuit, and the shape of the sections comprisingthe surface of the object. What is important is that a curved surface bedivided into a plurality of regions, and that those regions correspondto one or more screen or stencil segments used for applying the circuit.

FIG. 6 illustrates a fragment of a typical circuit which can be appliedby the present invention. Areas 62 comprise the regions where theconductive cermet has been laid down, and areas 61 comprise the regionswhere no cermet has been applied. FIG. 6 comprises only one example of acircuit pattern.

If the solid areas in FIG. 6 represent the conductive cermet material asapplied to the curved surface, either a screen or a stencil may be used.If, on the other hand, the solid areas are the open areas and thesurrounding areas are to be conductive cermet, only a screen can beused. This is because the screen is a fine wire mesh with an embeddedpattern that blocks the cermet from being transferred to the substratein the unwanted areas, whereas the stencil consists of completely openholes or shapes where the conductive cermet is transferred and solidmaterial where it is to be prevented from transferring to the substrate.Since, in FIG. 6, these solid areas would be islands, there would be nostructure to support these areas unless bridging spokes were permittedto hold the stencil together. These bridging spokes would then need tobe part of the clear areas of the pattern.

FIG. 8 provides a cross-sectional view of the structure of the presentinvention. Reference numeral 81 designates the surface of the object,such as the nose cone, onto which the circuit is to be applied.Dielectric layer 82 is applied to surface 81. Layer 82 may, in fact,comprise a plurality of layers of dielectric. Circuit elements 83 areapplied to the dielectric layer. The circuit is then covered bydielectric layer 84, which also may itself comprise a plurality oflayers of dielectric.

For purposes of illustration, the dimensions implied by FIG. 8 areexaggerated, and are not necessarily drawn to scale.

In one example, the thickness of the initial layer of dielectric may beabout 0.002 inches. The thickness of the fired cermet is typically about0.0005 inches. The cermet material tends to sink into the dielectric,because it contains metal and is heavier than the dielectric. The cermettherefore does not contribute appreciably to the overall thickness ofthe structure. When the final layer or layers of dielectric have beenapplied, the total thickness of the coating may reach or exceed about0.010 inches. The numbers given here are by way of example only, and arenot intended to limit the invention. In practice, the thickness of thedielectric layers and the number and placement of both the conductivecermet and dielectric layers are dictated by the circuit design and bythe required electrical and environmental performance.

In the examples discussed above, it was implied that the same screen orstencil segment is used multiple times on the same object. In the moregeneral case, it is possible to form different circuit patterns ondifferent sections of the nose cone or other object. Forming differentcircuit patterns at different locations can be done by providing anentirely separate fixture, with its own frame and screen or stencilassembly, of the type similar to that shown in FIG. 5. Or the differentpatterns could be produced by replacing the frame and screen or stencilon a single fixture by a different frame and screen or stencil assembly,defining a different circuit pattern. Indeed, one could have numerousfixtures and/or frames, providing different and distinct screen orstencil patterns, and the ogive nose cone, or other object, could bemoved from one fixture to another.

The following is a summary of a typical procedure for applying a circuitto a curved surface, according to the present invention.

First, the ogive nose cone, or other object to which the circuit is tobe applied, is inspected for surface defects. If the surface containsvarious open pores or cavities, the surface can be made smooth byskiving a dielectric paste material onto the surface, such that thepaste fills the pores. The object is then fired to seal and stabilizethe dielectric. If the surface is already very smooth, the above stepscan be omitted.

Next, the nose cone is sprayed with dielectric, dried, and fired to forma smooth dielectric ceramic skin having a typical thickness of about0.002 inches. This step could be performed in several iterations. Thatis, one could apply two or more layers of dielectric in the abovemanner. The ogive nose cone could be fired after each application ofdielectric.

When the desired thickness of dielectric has been built up, theconductive cermet is applied. As described above, for the case where theobject is an ogive nose cone, the cermet is preferably screened orstenciled onto every other section of the surface of the nose cone. Thenose cone is again fired, so that the metal particles in the cermet fusetogether to form conductive elements. As a result of firing, the cermetgenerally sinks into the dielectric layer so that the resultant layer isfairly smooth. The thickness of the fired cermet may typically be onlyabout 0.0005 inches.

The above process of screening or stenciling the cermet onto the nosecone is then repeated for the sections of the nose cone which did notpreviously receive cermet.

After all desired cermet has been applied and fired, the circuit isenclosed by spraying one or more layers of dielectric onto the object.Again, the application of this final, outer coating of dielectric can beapplied in one or more layers. If multiple layers are used, the objectmay be fired after the application of each layer, or after a group oflayers have been applied.

If multiple circuit layers, separated by dielectric layers, are desired,these circuit layers are applied in the same manner as describedpreviously for the single initial layer. For interconnection betweencircuit layers, screening or stenciling of the dielectric layer(s) inthe same manner, and the same fixturing scheme as described above forapplication of the conductive cermet, can also be accomplished. Toconnect the circuit layers electrically, vias are created that are voidof dielectric, and these are subsequently filled with the conductivecermet by screening or stenciling or skiving, as part of this invention.

The required final thickness of the outer dielectric layer depends onthe level of protection needed for the circuit layer(s), based on thenature of the environment into which the object is expected to travel.The desired thickness also depends on the electrical characteristics ofthe electronic circuitry which may be located inside, or made part of,the ogive nose cone, and which may be used for sending and/or receivingelectromagnetic signals. The circuit pattern defined by the cermet may,in one example, be designed to shield the internal circuitry frominterference from the outside, while permitting such circuitry tooperate as intended.

The invention can be modified in ways which will be apparent to thoseskilled in the art. The invention is not limited to use with particularobjects, but can be used whenever it is necessary to provide one or moreembedded ceramic circuit on a curved surface. Such modifications shouldbe considered within the spirit and scope of the following claims.

1. Apparatus for applying a dielectric layer to an object having acurved surface, the object having an axis of rotation, the object havinga diameter which varies along the axis of rotation, the apparatuscomprising: a) a spray head including a reservoir for holding adielectric material, capable of being fired at high temperatures, andhaving a viscosity sufficiently low to enable the dielectric material tobe sprayed onto an object, b) the spray head being mounted to a supportwhich is connected to a plurality of motors which enable the spray headto move with three degrees of freedom, c) means for rotating the objectat all times while the spray head is spraying the dielectric material,and d) computer means programmed to control both movement of the sprayhead and rotation of the object, wherein the computer means comprisesmeans for dynamically positioning the spray head in three dimensions,such that the spray head is held perpendicular to, and at a controlledand constant distance from, the surface of the object while thedielectric is being sprayed, wherein the computer means also includesmeans for varying a rotational speed of the object, while the object isbeing sprayed, wherein the speed of rotation is coordinated, by saidcomputer means, with movements of the spray head, so as to deposit auniform thickness of dielectric per unit time onto the surface of theobject, and means for heating the object before the spraying step hasbegun, and for heating the object continuously while the object is beingsprayed with the dielectric material, in an amount sufficient such thatthe dielectric material dries upon contact with the object.
 2. Theapparatus of claim 1, wherein the computer means comprises means forcontrolling the spray head so as to deposit a plurality of layers of thedielectric material onto the object.
 3. The apparatus of claim 1,wherein the dielectric is sprayed onto the object in a layer having athickness, after firing, of about 0.002 inches.